Squirrels are hugely destructive and need getting rid of.
Assuming it is a grey (reds are protected) ask your council for advice. Or your insurance company.
You could buy a trap and bait it - peanut butter is a favourite. You then have the problem of what to do with it - it is illegal to release vermin (the grey squirrel is classed as vermin) in the UK. You will have to kill it - drown it in a water butt is the usual method with my neighbours. Or shoot it.
Poison is dodgy especially if you have cavity walls - it is likely to hide away deep in a cavity to die and then you have to find the stinking, rotting carcass.
More sentimental people play loud music in the loft space and leave a light on for 48 hours. Cloths soaked in Jeyes Fluid also help drive the squirrel away as they cannot abide the smell.
When you are sure he has gone you have to block the access holes up - or he will be back.
Good luck!